Electron paramagnetic resonance of n-type silicon for application in 3D thermometry

While there are several 2D thermometry techniques that provide excellent spatial, temporal and temperature resolution, there is a lack of 3D thermometry techniques that work for a wide range of materials and offer good resolution in time, space and temperature. X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) imaging can provide 3D temperature information. However, XRD is typically limited to crystalline materials while NMR is largely limited to liquids where the resonance lines are sufficiently narrow. We investigate electron paramagnetic resonance (EPR) of n-type silicon as a possible means of 3D thermometry. The temperature dependence of the spin-lattice relaxation rate (1/T₁) of conduction electrons in n-type Si have been extensively studied for low dopant concentrations and follows a T³ law due to phonon broadening. For heavily-doped Si, which is desirable for good signal to noise ratio (SNR) for application in thermometry, impurity scattering is expected to decrease the temperature dependence of 1/T₁. However, the effect of impurity scattering on the spin-lattice relaxation rate, or equivalently the EPR linewidth, at temperatures approaching room temperature and high carrier concentrations has not been experimentally studied. Our results show that, in heavily doped n-type Si, spin-lattice relaxation induced by impurity scattering does not drastically decrease the temperature dependence of EPR linewidths. In P-doped Si with donor concentration of 7 × 10¹⁸ /cm³, the EPR linewidth has a T^5/2 temperature dependence; the temperature dependence decreases to T^3/2 when the donor concentration is 7 × 10¹⁹ /cm³. While the temperature dependence of linewidth decreases for heavier doping, EPR linewidth is still a sensitive thermometer. Our results show that EPR linewidth can be a sensitive thermometer for application in 3D thermometry with systems embedding microparticles of heavily doped n-type Si.